Add Stop Limit orders

[ppamorim]

In this PR I am including these functions:

• stop_limit_sell_order

• test_stop_limit_sell_order

• stop_limit_buy_order

• test_stop_limit_buy_order

  It also include more concise types like:

• OrderType

  • Limit
  • Market
  • StopLossLimit

• OrderSide

  • Buy
  • Sell

I also removed unnecessary conversion from Data -> String -> JSON, now the library converts Data -> JSON directly and the code got simplified.

I have updated some libraries, please let me known if you want to revert this change.

[dorak88783]

I think your cleanup is cool, I didn't review all the details yet, but it's nicer if that would be a separate PR.

If you want you could make a new branch, git cherry-pick the commits that only refactor code, and make a separate PR.